This invention relates to the use of micro-electrode arrays in biosensors and to methods of producing such biosensors.
An array of micro electrodes offers many advantages over a large area electrode for use as an amperometric electrochemical sensor. These advantages include a very small charging capacitance, radial diffusion kinetics, a rapid response time and easily interpreted current-voltage behaviour. The present invention relates to a particular arrangement of such an array to provide a biosensor.
The present invention provides a biosensor comprising a conducting surface, a layer of dielectric material overlying the conducting surface, a plurality of micro electrodes constituted by a plurality of pores extending through the thickness of said dielectric layer, each pore being separated from its neighbour, a biopolymer positioned in said pores, and a counter electrode arranged such that electrical connection can be made between it and at least part of said conducting surface by a fluid to be assessed.
The present invention also provides a method of making a biosensor comprising the steps of:
providing a conducting surface;
providing a layer of dielectric material adjacent to said conducting surface, said dielectric material comprising a plurality of pores extending through the thickness of the dielectric layer, each pore being separated from its neighbour;
providing a biopolymer in said pores, and
providing a counter electrode insulated from said conducting surface.
In general, the biosensor comprises one or more areas of conducting material arranged on an insulating substrate. Adjacent to each area of conducting material is a dielectric coating which comprises a plurality of pores. These pores are the micro electrodes that convert a chemical response into an electrical signal. They do this due to the presence of a biopolymer immobilised on the conducting surface. In use, a fluid to be assessed is applied to the pores in the dielectric surface so as to be in contact with the biopolymer immobilised in the pores. A counter electrode is also provided so as to be in electrical connection with at least one of the conducting areas via the fluid being assessed. A constant voltage may be applied between the counter electrode and the conducting area and the current that flows therebetween may be measured. Any such measured current is indicative of the amount of a chosen compound in the assessed fluid. Different biopolymers may be used to allow different compounds to be measured giving great flexibility. The biosensor device typically has dimensions of a few millimeters although it could of course be made smaller or larger, depending on the intended application.
The electrodes typically have areas of 1 to 100 xcexcm2 and are typically separated by distances of about ten times their diameter. The surface of the electrode can be functionalised with various biopolymers, especially enzymes such that they will only give an electrochemical response to a specific compound (or analyte). Other biopolymers include other proteins, as well as nucleic acids, lipids and polysaccharides. For example, enzymes that respond to important body fluid components such as lactate, glucose, creatine, or various antibodies could be used. Typical enzymes include lactate dehydrogenase, glucose dehydrogenase, cytochrome P450 and mutants of the aforesaid enzymes. In addition by ociation of these enzymes, antibodies, nucleic acids, lipids and polysaccharides can be made electrochemically active. Micro-electrode arrays have not, it is believed, previously been activated by biopolymers for use as biosensors. One advantage is that only two electrodes are required vis the working electrode and a counter electrode. Although the magnitude of the current from an individual micro-electrode is low, this can be offset by an improved signal to noise ratio if an array of hundreds or thousands of individual micro-electrodes is used. This is because the signal to noise ratio increases as the square root of the number of individual micro-electrodes.
Reference will now be made, by way of non-limitative example, to the accompanying drawings in which: